Adjustable-torque restraining mechanism



Nov. 12, 1963 J. F. VALENT] 3,110,366

v ADJUSTABLE-TORQUE RESTRAINING MECHANISM Filed Jan. 25, 1962 3,119,366 ADJUSTABLE-TORQUE RESTRAEJENG WCHANEM Joseph F. Valenti, North Babylon, .Y., assignor to Fairchild Camera and instrument Corpcration, a corporation of Delaware Filed San. 25, 1952, Ser. No. 163,75l Claims. .(Cl. 138-83) This invention relates to adjustable-torque restraining mechanisms and, while it is of general application, it is particularly suitable for embodiment in a rotatable adjustable electrical impedance element, for cramp-lea potentiometer, and will be specifically described in such an embodiment.

In the application of rotatable electrical impedance elements to various control systems, it is frequently required that an element be adjusted by a servo mechanism capable of delivering a torque of only a specified value so that the specifications for the impedance element frequently include a limiting torque required to adjust the element. Moreover, in the case of manually adjustable impedance elements, it is highly desirable that the element be capable of adjustment in response to some given limiting applied torque, since otherwise, when it is a tempted to make a very small adjustment, it is difiicult to avoid jerky movements which tend to impair the accuracy of adjustment.

In addition, impedance elements having similar electrical characteristics are often useful in different systems and different environments which may require different limiting adjusting torques. I

At the same time, such adjustable impedance elements are often incorporated in systems subject to vibration, shock, and acceleration forces. in such cases, the specifications for the elements usually set a lower limiting value of torque to ensure that the element will certainly not be adjusted by such extraneous forces. Therefore, in such applications, it is customary to specify a range of torques below which the element certainly will not be adjusted and above which it certainly will be adjusted. It is desirable, of course, that this torque range be as narrow as feasible.

In prior adjustable impedance elements of the type described, it has not been possible to predetermine or preset this range of torques with any degree of accuracy and it has not been possible to adjust the torque range once the design of the element is completed. Therefore, it has been necessary either especially to design the impedance element for the particular torque range required or to maintain an inventory which includes a large number of impedance elements of duplicate electrical characteristics but having a number of different torque ranges. Such an arrangement is, of course, costly and cumbersome.

it is an object of the invention, therefore, to provide a new and improved adjustable-torque restraining mechmisrn which obviates one or more of the above-mentioned disadvantages of prior art devices of this type.

It is another object of the invention to provide a new and improved adjustabletorque restraining mechanism by means of which the range of applied torques below which the device will certainly not operate and above which it will certainly operate may be readily predetermined and in which such range may be shifted over a relatively Wide range'of torques.

In accordance with the invention, there is provided in a rotatable electrical impedance apparatus, an adjustabletorque restraining mechanism comprising a frame, a supporting shfit for an element of the impedance apparatus journalled in the frame, an abutment element unitary with the supporting shaft, and at least one friction washer in- United Sates Patent 0 3A lh-fihfi Patented Nov. 12, 1963 terposed between the frame and the abutment element. The mechanism further comprises a compression spring surrounding the shaft and urging the abutment element and the frame apart and a plurality of threaded elements adjustable to adjust the compression of the spring, thereby to adjust the frictional drag on the shaft upon its rotation. The term unitary element, as used herein and in the appended claims, refers to an element which comprises a single integral structure or a plurality of structural elements rigidly secured together.

For a better understanding of the present invention,

together with other and further objects thereof, reference is bad to the following description taken in connection with the accompanying drawing, while its scope will be pointed out in the appended claims.

' Referring now to the drawing:

The single FIGURE is a cross-sectional detail view of an adjustable-torque restraining mechanism embodying the invention as applied to an adjustable potentiometer. 7

Referring now more specifically to the drawing, there is represented a rotatable electrical impedance apparatus, such as an adjustable potentiometer, including a frame 1t? having an inturned hub or abutment 19a with a plane surface 1% normal to the axis of the frame. In the embodiment shown, the frame 11} is made in anumber of sections joined by clamping rings ll, 11, etc., the number of sections being determined by the particular application. Within each section is disposed one of the potentiometer-rings or cards 12, 12, etc., adapted to be engaged by its respective one of the rotatable contacts13, 13 secured to but insulated from a shaft 14. Also mounted on the shaft 14 and insulated therefrom are collector rings 15, 15 engaged by brushes 16, 16 connected to external terminals 17, 17, the collector rings 15, 15 being electrically connected to the contacts 13, 13.

The details of the electrical potentiometer per se, other than the restraining mechanism to be described, form no part of the present invention. However, the potentiometer unit, per se, may have the general construction of that described in Patent No. 2,592,392 to Canziani et al.

Thus, the shaft 14- supports the contact elements 13, 13 of the adjustable impedance element as well as the collector rings 15, 15 included in the electrical connections to the external terminals 17, 17. The shaft 14 is suitably journalled in the frame 19, as by sleeve bearlugs 18, 13, and has a protruding portion for connection to any suitable operating mechanism. The shaft '14 has an abutment element unitary with the shaft, specifically a collar 19 having a hub 19a secured to the shaft 14, as by a set screw 2%. As shown, the abutment element '19 abuts a collar 21 mounted on the shaft 14 but spaced therefrom by a washer 2.2 of insulation material.

The torque-restraining mechanism of the invention also includes at least one friction washer interposed between the frame 10 and the abutment element 19. Specifically, there are provided a pair of friction washers 23, 23a mounted on the shaft 14 and an intervening metallic washer 24, the washer 23 being disposed adjacent the hub 19a and the washer 23a engaging the abutment ltla of the frame 1%.

The torque-restraining mechanism further includes a helical compression spring 25' surrounding the hub 19a and, therefore, surrounding the shaft 14, and urging the abutment element 19 and the abutment 10a of the frame it) apart. Specifically, the spring 25 engages and urges apart the abutment element 19 and the adjacent friction washer 23. Preferably, the spring 25 has a relatively high spring constant and its end turns are ground or otherwise suitably finished to plane surfaces for engagement washer 22.

' able to adjust the compression of the spring, such as 'a plurality of set screws 26, 26 symmetrically disposed in the abutmentltla about the shaft 14. The screws 26 engage the washer 23a and, by equal adjustments, are effective to adjust the compression of the spring 25.

It is believed that the operation of the adjustable-torque restraining mechanism of the invention will be apparent from the foregoing description. Sincethe abutment element 19 is secured to shaft 14 by set screw 29, obviously rotation of the abutment element carries with it the As stated above, washers 23, 23a, and 24 loosely fit the shaft 14 so that they may be said to be floating. Therefore, which of these several washers actually turns upon rotation of shaft 14 depends upon which interfaces develop the least frictional drag. Ordinarily, the adjusting screws 26 will slightly bite into the 'plastic friction washer 23a and prevent it from rotating. Similarly, the restricted surface of the flattened end of the spring 25 will ordinarily. develop a considerable friction with the adjacent face of the Washer 23. Consequently, the least frictional drag occurs at the interfaces between the stainless steel Washer 24 and the plastic friction washers 23 and 23a and this is the frictional drag which determines the restraining torque on shaft 14. Slippage may occur at either or both of these interfaces. The use of the friction Washer 22 and the pair of friction washers 23, 23a and the intervening metallic washer 24 provide a frictional drag on rotation of the shaft 14 which is rather readily predeterminable and stable. By adjust ment. of the screws 25 from the condition in which the spring 25 is compressed scarcely at all to the condition Where the spring 25 is substantially compressed, the restraining torque on the shaft 14 may be adjusted to any predetermined setting within a wide range and, once set, will maintain that value of restraining torque with a high degree of reliability.

While the adjustable-torque restraining mechanism of the invention may, of course, utilize frictional drag elements of any of a Wide range of sizes and materials having different coeflicients of friction, there follow the specifications for one particular group of elements which have been found satisfactory in practice:

While there has been described what is, at present, considered to be the preferred embodiment of the invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention and it is, therefore, aimed in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention.

What is claimed is: V 1. In a rotatable electrical impedance apparatus, an adjustable-torque restraining mechanism comprising:

(a) a frame;

(17) a supporting shaft for an element of the impedance apparatus journalled in said frame;

() an abutment-element unitary with said shaft;

(d) at least one friction washer interposed between said frame and said abutment element;

(e) a compression spring surrounding said shaft and urging said abutment element and said frame apart;

(1) and a plurality of threaded element adjustable to adjust the compression of said spring, thereby to adjust the frictional drag on said shaft upon its rotation.

2. In a rotatable electrical impedance apparatus, an

adjustable-torque restraining mechanism comprising:

(a) a frame having an abutment;

(b) a supporting shaft for an element of the impedance apparatus journalled in said frme;

(c) an abutment element unitary with said shaft;

(d) a pair of friction Washers and an intervening metallic washer interposed between said frame and said abutment element;

(e) a compression spring surrounding said shaft and urging said abutment element and said frame apart;

(f) and a plurarity of threaded elements adjustable to adjust the compression of said spring, thereby to adjust the frictional drag on said shaft upon its rotation.

3. In a rotatable electrical impedance apparatus, an

adjustable-torque, restraining mechanism comprising:

(a) a frame having an abutment;

(b) a supporting shaft for an element of the impedance apparatus journalled in said frame;

(0) an abutment element unitary with said shaft;

- (d) a pair of friction Washers and an intervening metallic washer interposed between said frame and said abutment element;

(e) a compression spring surrounding. said shaft and urging said abutment element and the adjacent one of said friction Washers apart;

(7) and a plurality of threaded elements adjustable to adjust the compression of said spring, thereby to adjust the frictional drag on said shaft upon its roration.

(b) a supporting shaft for an element of the impedance apparatus journalled in said frame; I

(c) an abutment element unitary with said shaft;

(d) a friction washer engaging said frame;

(e) a compression spring surrounding said shaft and urging said abutment element and said friction washer apart;

(7) and a plurality of threaded elements adjustable to adjust the compression of said spring, therebyto adjust the frictional drag on said shaft upon its rotation.

5. In a rotatable electrical impedance apparatus, an

adjustable-torque restraining mechanism comprising:

(a) a frame;

(b) a supporting shaft for an element of the impedance apparatus journalled in said frame;

(c) an abutment element unitary with said shaft;

(a') a friction washer engaging said frame;

(2) a compression spring surrounding said shaft and urging said abutment element and said friction washer apart;

(1) and a plurality of screws engaging said friction washer and adjustable to adjust the compression of said spring, thereby to adjust the frictional drag on said shaft upon its rotation. 1 I

References Cited in the file of this patent FORElGN PATENTS 4. In a rotatable electrical impedance apparatus, and

Starkey Ma 25, 1926' 

1. IN A ROTATABLE ELECTRICAL IMPEDANCE APPARATUS, AN ADJUSTABLE-TORQUE RESTRAINING MECHANISM COMPRISING: (A) A FRAME; (B) A SUPPORTING SHAFT FOR AN ELEMENT OF THE IMPEDANCE APPARATUS JOURNALLED IN SAID FRAME; (C) AN ABUTMENT ELEMENT UNITARY WITH SAID SHAFT; (D) AT LEAST ONE FRICTION WASHER INTERPOSED BETWEEN SAID FRAME AND SAID ABUTMENT ELEMENT; (E) A COMPRESSION SPRING SURROUNDING SAID SHAFT AND URGING SAID ABUTMENT ELEMENT AND SAID FRAME APART; (F) AND A PLURALITY OF THREADED ELEMENT ADJUSTABLE TO ADJUST THE COMPRESSION OF SAID SPRING, THEREBY 